John henry dallmeyer of london



J H DALLMEYER LENS FOR PHOTOGRAPHIG PORTRAITURE.

Patented June 11, 1867.

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JOHN HENRY DALLMEYER, OF LONDON, ENGLAND.

Letiera Patent No. 65,729, 41.1w June 11, ism.

COMPOUND LENS FOR PHOTOGRAPH G PORTRAITURE.

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TO ALL TO WHOM IT MAY CONCERN:

Be it known that 1, JOHN HENRY DALLMEYER, of 19 Bloomsbury street, inthe county of Middlesex, England, optician, a subject of the Queen ofGreat Britain, have invented or discovered certain new and usefulImprovements in Compound Lenses Suitable for Photographic Uses andl, thesaid JOHN HENRY DALLMEYI-IR, do hereby declare the nature of the saidinvention, and in what manner the same is to be performed, to beparticularly described and ascertained in and by the following statementthereof; that is tosay- My invention relates to double combination andother lenses or objectives intended chieily for portraiture, but alsoapplicable for views and etherpietures, and consists in arranging themso that the lenses composing one of the combinations are of such formand so positioned that by a slight variation of distance or separationbetween its elements, any desired amount of spherical aberration can beobtained, without at the 'same time materially deranging-the othernecessary corrections of a photographic objective or lens. With a lensor objective so constructed the operator can, by sacrificing intensesharpness of definition on one plane, distribute the definition overseveral planes, and so obtain a more artisticand pleasing result.

A double combination lens or objective may be constructed according tomy invention, as is shown at Figure 1. It diilers from doublecombination portrait lenses (such as that originally invented byProfessor- Petzval of Vienna, and shown at Figure 2,) in that the lensescomposing the back combination are reversed, both as regards their orderof position and form, 2'. (1., the flint-glass lens is exterior ornearest the screen or image, and the crown-glass lens is nearest to orfaces the front combination, whilst at the same time the radii ofcurvatures of, the adjacent surfaces of the crown and flint-glass lensesare dissimilar, and suitable means are provided to alter the distance orseparation between these two lenses at will. The-infer my new lens, theratio of effective aperture of which late the compound focal length ofthe entire combination as 1: 3, the angle of field embraced about sixtydegrees, and the image free from distortion, the details of constructionare as follows,

reference being made to the annexed diagram, fig. 1.

For a given compound or equivalent focal lengtinf, of the entirecombination or objective, I construct two combinations, as A and 13,both of the same diameter, equal to f.,. The ratio of focal length ofthe anterior combination A is to the compound focusf as 9 .6, and thefocal length of the back combination B is to A as 3 2. The front oranterior combination A is composed of adouble-convex lens of crownglass, a, and adorableconcave lens of flint glass, 6. The radius ofcurvature of the anterior surface, r,, of the crown lens a, is inproportion to the compound focusfof the entire combination or objectiveas 1. 2, and the external radius of curvature, 9-,, of-fiint-glass lensI), is to 1', as 5 1. The internal radii of curvature, 17 of crown lensa, a'nd1 of flint lens 6 are, by preference, identical and cemented, andsuch that for the above focal length the combination A, by preference,is achromatic, or nearly so, which, for the qualities of glass employedby me, is the case when the ratio of radii between the anterior andinternal surfaces, 2. 6., r, and r, of crown lens a, is as 31 27. At adistance equal to the diameter of the front combination A, is situatedthe posterior combination B, composed of two lenses, viz, of, bypreference, a meniscus lens of crown glass, 0/, with the concave surfacefacing the front combination, and of a OGDCCtVO-COUVGX lens of flintglass, in, convex side outside or facing the screen of the camera, thesetwo lenses having their adjacent surfaces dissimilar. The radius ofcurvature of the adjacent or internal convexsurface, 9-,, of crown lensa", is in proportion to the radius of curvature of the anterior surface1-, of crown lens a as 2 3, and the posterior or external radius ofcurvature 9', of flint lens 6, is to 1', as 37 31. The radii ofcurvatures of the other two surfaces, viz, the concave surface a, ofcrown lens (1 and the concave surface 1, of flint lens I), are such,that for the above focal length and the lenses a and b, by preferenceseparated from each other, (2'. 0., the distance between the centres oftheir adjacent surfaces 2, and 0- by an interval, 0 equal tofcombination 1? is achromatic or actinic,. or nearly so. For thequalities of glass employed by me, this is the case when the ratio ofradii crown lens a is 1', :13 as 1 16, and that of the flint-glass lens6, 1-,, r r, as 2 1 nearly.

The combination or objective constructed as above, without anydiaphragm, and with the component lenses of combination B as separatedabove, viz,,at adistanee equal to]",,,, is free from spherical andchromatic aberration for both the axial and oblique pencils, but byincreasing the separation or distance between the lenses composingcombination B, (between the limits, say of f tof,,,) suitable means,such as a screw, being provided for the purpose, the correction forspherical aberration for the entire combination or objective is therebyim-pairedfor the moment to any required extent, or what may be termeddifi'usion of definition obtained to suit the wishes of the operator forthe time being, without at the same time materially deranging the othernecessary corrections of the lens or objective, and this has never beenaccomplished heretofore. I observe also that the particulars ofdimensions and proportions given as above arc those best suited toaccomplish the particular object in view, but for other objects, such asa combination possessing greater intensity or rapidity, or one to haveless intensity or rapidity than the combination herein described, otherdimensions may be employed.

The improvements of any lens, constructed as above described. overexisting double combination portrait lenses are these, viz:

First. Capability of adjustment at the will of the operator, to obtainfor the moment any desired amount of distribution of definition overseveral planes, simply by an alteration in the distance or separation ofthe elements composing, as in the lens described, the back combination,without at the same time dcranging the other necessary corrections ofthe entire objective.

.Second. With the lenses composing the combination at their normaldistance apart, more perfectcorrection of the oblique or marginalpencils for both the spherical and chromatic aberrations.

Third. Greater equality of illumination throughout the entire surfacecovered by the lens.

Fourth. Entire freedom from distortion without the aid of diaphragms,and greater flatness ol' field.

Fifth. Greater adaptability to varying purposes of one and the same lensor combination.

Sixth. Economy as regards the optical means employed.

With the same object of regulating the sphericalaberration at pleasure,a combination similarly constructed to the posterior combination in fig.2, may be made to form'part of other lenses or objectives composed ofmore than two combinations, such as the triplet. Also, (but'lessconvenieutly,) the regulation of the spherical aberration may beobtained by means of the anterior cembinationof a double combination, inwhich case the anterior combination is made with the adjacentsurfaces-of its elements of different curvatures, and with the flintlens outside or towards the view. Means are provided for slightlyaltering the distance between those elements at pleasure.

What I claim, is-

The construction of lenses or objectives suitable for photographicpurposes, the componentparts of which are of such form and so positionedthat by a slight variation of distance between the lenses of one of thecom.- binations (as by means of a screw-movement,) the operator canproduce at will any desired amount oi spherical aberrations or diffusionof focus, without at the same time materiallydcranging the othernecessary corrections of a photographic lens, substantially as hereindescribed.

I also claim the combining lenses a a b b, substantially as hereindescribed.

I H. DALLMEYER.

Witnesses:

G. F. bVARRIJN, Jenn DEAN, Jenn Hannrson, Notary Public.

[Both of N0. 17 Graceclutrch Street, London.

